Multiplex radio communication



MULT IPLEX RADIO COMMUNI CATION R Filed Jan. 21, 1932 SUPEE SON/C OSC/L L 4 702 mam .fZLoZZ 1' '1, 2"

J9 awez Patented May 11, 1937 UNITED STATES MULTIPLEX RADIO CORBVIUNICATION William Arthur Loth and Armand Joseph Givelet, Paris, France Application January 21, 1932, Serial No. 588,028 In France January 23, 1931 3 Claims.

The present invention is directed to a system of multiplex radio-telephony and radio-telegraphy characterized by the fact that a single highfrequency carrier wave, called the primary fre- 5 quency, is modulated or controlled or commutated by one or more lesser intermediate generated frequencies, called secondary or commutating frequencies. These messages are received on a radio-telegraph or radio-telephone receiving set, with or without amplification. The receiving set is instantaneously tunable at will to the primary carrier wave.

In one embodiment of our invention, the signals which it is desired to receive are produced at successive instants, but only one signal is produced at a given instant, each signal being so to speak out off or interrupted or decapitated or commutated in activity at each occurrence during a very short interval, so that they are separated from each other by intervals which are likewise very short and are staggered. Thus the ear, by

virtue of a kind of inertia of its parts, receives a continuous sensation, which makes it possible to receive simultaneously as many diiferent mes- 5 sages as there are diiferent messages being transmitted.

One embodiment of the system mentioned above can be realized by an apparatus which has moving mechanical elements, or by an apparatus which is entirely static. In the case of the mechanical elements, the circuit of the transmitting antenna terminates in a distributing element which is movable and which engages or makes contact successively with other elements, these latter elemerits appertaining respectively to circuits of each of which a microphone forms a part.

synchronism of the interruption or commutation at transmitter and receiver can be obtained by means of synchronous motors which can be 40 connected to the same commercial supply system. It is also possible to employ any suitable arrangement, such as those heretofore known in the art, for instance, very accurately regulated clock movements, maintained in synchronism by continuous or intermittent transmission of a synchronizing wave, as is used for the hourly regulation of clocks by radio.

Other objects of the invention will be obvious and in part pointed out hereafter.

In order that the invention and its mode of operation may be readily understood by persons skilled in the art, we have in the accompanying illustrative drawing and in the detailed following description based thereon, set out several possible embodiments of the same.

In the drawing:

Fig. 1 shows a multiplex telephone system in which the spacing of active intervals of the application of each voice channel is obtained by using supersonic alternating current supply in a push-pull arrangement.

Fig. 2 shows a multiplex transmitting system in which duplicate transmitters have their plates supplied by alternating current of supersonic frequency, connected in push-pull, and each transmitter in turn has two generating tubes connected in push-pull.

It is also possible to have a stator element receive high-frequency modulated currents which it will then in turn deliver to the antenna. In this case, it is possible to employ a rotating device which acts by electro-static induction. For example. the stator can carry the fixed plates of a variable condenser while the rotor carries the movable plates, which successively arebrought into electrostatic relation with the fixed plates.

Very short interruptions can be obtained by a static system not involving mechanically moving elements, but involving only elements at rest, arranged as follows:

When the plate of a transmitting tube is supplied by an alternating current of supersonic frequency, that is one beyond the audible range, then when a conversation is transmitted from the sending station there is produced at the receiving station a sensation of continuity notwithstanding the fact that in reality the current is interrupted a large number of times each second caused by the negative halves of the cycles.

These negative halves of the cycles which are not used in such an arrangement, can be utilized by placing two transmitters at the same time on the same wave length and by connecting the circuits together in such manner that thetwo tubes are alternately in operation, one tube being in operation while the other tube is out of operation. To obtain this result, there is employed a plate supply transformer having a mid-tap on the secondary, the mid-point being connected to the filaments of the tubes.

Fig. 1 shows the connections of the tubes so arranged. According to this figure, the plates of the tubes L and L are supplied by the transformer T having its secondary s divided into two equal parts with an alternating voltage of superi sonic frequency. Each terminal of this secondary is connected to the plate of one of the tubes L or L so that alternately-one plate is negative when the other is positive, and vice versa. The connections of these tubes are made as usual.

The output of each of the microphones A and B is respectively delivered to the grid of its corresponding tube in any suitable manner.

At the receiving station, a similar arrangement is employed, but the microphones are replaced by telephone receivers. It is absolutely necessary that the supersonic alternating current supplied at the receiving station shall exactly correspond to the supersonic plate current supply at the transmitting station. In reception, in order to obtain the desired result, it is also sufficient to apply the alternating potential to the grid, and to make the grid of a tube alternativelylpositive and negative, instead of the plates.

If the current supply is'taken fromthe same power distribution system at both the transmit ting station and the receiving station, the problem is easy to solve. If this is not possible, use may be made of a synchronizing wave, and one synchronizing wave can serve for an entire radio broadcasting system of stations, for instance, a 10,000 meter wave corresponding to 30,000 cycles, which meets the requirements of an ultra-audible frequency.

By employing such an arrangement of tubes so connected, all of the signals transmitted from a system are doubled. Two-way radio-telephony can thus be carried on if one-half of the secondary of the supply transformer is connected to a transmitter, and the other half to a receiver; then in one station the transmitter is in operation at the same time as the receiver in the other station. A method will be later described for obtaining the synchronizing frequency without using a special wave.

It is likewise possible to obtain two simultaneous communications by making the grids of the tubes alternately positive and negative, by means of a similar arrangement. Any other form of device for dividing potential can be employed instead of the transformer above described.

In these arrangements, it may become advantageous to employ duplicate transmitters having symmetrical circuits and to apply the supply potential of the plate or grid to the nodal point of these symmetrical circuits. By this arrangement, the telephone current, voice or music, cannot pass through the source or generator which supplies the ultra-audible frequency. Figure 2 shows such an arrangement. P1 and P2 are two identical or duplicate transmitters or generating units having symmetrical circuits and each comprising two generating tubes L1, L1 and L2, L2. The grids of the respective pairs of tubes are connected by the grid circuits comprising the grid coils J and J. The speech inputs of the microphones are delivered at the respective input terminals A and B, and are applied between the filaments of the tubes and the center points of grid coils J and J. The plates of tubes L1 and L1 are connected through plate coil K, and the plates of coils L2 and L2 are connected through plate coil K. The respective center points M and M, of plate coils K and K, are connected through the coil S which is the secondary of the transformer Z. The mid-point M of the secondary S is connected tov the filaments of the tubes, in a manner similar to that shown in Fig. 1.

The grid coil J is in inductive relation with the plate coil K in the manner shown, and these coils constitute transformer T. The grid coil J is likewise in inductive relation with the plate coil K in the manner shown, and these coils constitute transformer T. 1 i

The local oscillator H generates a supersonic frequency, as has been described above, such as 30,000 to 50,000 cycles. This is delivered to the primary R of transformer Z, and through the secondary S is alternately applied to the points M and M of the plate coils. These points M and M by reason of the symmetry of their respective units are nodal points of the units P1 and P2 andare at zero radio-frequency potential with reference to the radio-frequency potentials of P1 and P2. The supersonic supply frequency from H is applied in phase opposition to the two nodal points M and M, and H thus acts as a balancer.

Since secondary winding S is connected between points M and M which are respectively nodal points of generating units P1 and P2, and are each at zero radio-frequency potential, no radio-frequency potential is applied to the terminals of the secondary winding S, and no current of radio-frequency flows therein.

Therefore no current of radio-frequency can reach the supersonic oscillator H. The voice frequencies delivered to voice input terminals A, B, can reach the plate coils only as the modulating frequency of the modulated radio-frequency current. The speech frequency input voltage is connected at the mid-point of grid coil J, and is applied to the grids of tubes L1 and L1 by the conductive paths extending in opposite directions from the mid-point of grid coil J through its two parts. In plate coil K the net result due to direct audio-frequency induction from J to K is zero, and no current of audio-frequency flows in K as such. Since no radio-frequency current flows in S, it is not possible for the voice frequency currents in any way to reach oscillator H, and no interference from voice frequencies can be caused in supersonic oscillator H.

The alternating current of supersonic frequency delivered from secondary S to plate coil K divides at M and flows in two opposite directions, as indicated by arrows f1 and f2. At a given instant, therefore, the currents of the supersonic frequency induced in the two halves of grid coil J by feed back from plate coil K to plate coil J are in phase opposition, and the net result is that the output delivered by the plates of tubes L1 and L1 to plate coil K contains no supersonic frequency due to feed back of the supersonic frequency supplied by H, from the plate coil to the grid coil. A similar condition obtains in unit P2.

Any known system of modulation can be employed. The oscillator producing the carrier wave need not be of the symmetrical type. Frei quency control can be secured by a master oscillator or by a quartz crystal.

If it is desired to employ a longer carrier wave, this can be done by restricting the band of frequencies which are produced by modulation. This restriction can be obtained by a filter which preferably allows the central part of this band to pass, and cuts off its ends. A particular form of this filter which can be used is a resonance amplifier of several stages having resonance which is more or less attenuated.

Use of a longer wave length is also made possible by heating with a local oscillator, with amplification and restriction of band Widths, in the manner which has just been described.

It is also possible to use the harmonics of a fundamental transmitted frequency for the secondary or commutating frequencies. Our system is very effective in operation to successfully attain multiplex radio communication. It will be obvious to those skilled in the art that our invention is susceptible of various modifications, and such modifications we consider comprehended within the spirit of our invention.

We claim:

1. In a radio communication system, a transmitting station and a receiving station, said transmitting station comprising a pair of duplicate generating units adapted to generate the same radio frequency, each of said generating units comprising a pair .of similar radio-frequency generating tubes and a transmitter plate coil connected between the plates of the two tubes comprised in said unit, a first winding constituting a source of alternating current of supersonic frequency, the point of said first winding of potential mid-way between the potentials of its terminals being connected to the filaments of the tubes of both of said generating units, the terminals of said winding being respectively connected to the respective mid-points of said plate coils, said receiving station comprising a pair of duplicate receiving units, each of said receiving units comprising a pair of similar receiving tubes and a receiver plate coil connected between the plates of the two receiving tubes comprised in said unit, a second winding constituting a second source of alternating current of supersonic frequency, the point of said second winding of potential mid-Way between the potentials of its terminals being connected to the filaments of the tubes of both of said receiving units, the terminals of said second winding being respectively connected to the respective mid-points of said receiver plate coils, and means for maintaining the frequency and phase of said second source at said receiving station identical with the frequency and phase of said first mentioned supersonic source at said transmitting station.

2. In a radio communication system, a transmitting station and a receiving station, said transmitting station comprising a pair of duplicate generating units adapted to generate the same radio frequency, each of said generating units comprising a pair of similar radio-frequency generating tubes and a transmitter plate coil connected between the plates of the two tubes comprised in said unit, a first winding constituting a source of alternating current of supersonic frequency, the point of said first winding of potential mid-way between the potentials of its terminals being connected to the filaments of the tubes of both of said generating units, the terminals of said winding being respectively connected to the respective mid-points of said plate coils, each of said generating units further comprising a grid coil connected between the grids of the two tubes comprised in said unit, a source of audio-frequency signal potential, and means for applying said audio-frequency potential between the mid-point of said grid coil and the 3 filaments of said tubes, said receiving station comprising a pair of duplicate receiving units, each of said receiving units comprising a pair of similar receiving tubes and a receiver plate coil connected between the plates of the two receiving tubes comprised in said unit, a second winding constituting a second source of alternating current of supersonic frequency, the point of said second winding of potential mid-way between the potentials of its terminals being connected to the filaments of the tubes of both of said receiving units, the terminals of said second winding being respectively connected to the respective mid-points of said receiver plate coils, and means for maintaining the frequency and phase of said second source at said receiving station identical with the frequency and phase of said first mentioned supersonic source at said transmitting station.

3. In a radio communication system, a transmitting station and a receiving station, said transmitting station comprising a pair of duplicate generating units adapted to generate the same radio frequency, each of said generating units comprising a pair of similar radio-frequency generating tubes and a transmitter plate coil connected between the plates of the two tubes comprised in said unit, a first winding constituting a source of alternating current of supersonic frequency, the point of said first winding of potential mid-way between the potentials of its terminals being connected to the filaments of the tubes of both of said generating units, the terminals of said winding being respectively connected to the respective mid-points of said plate coils, said receiving station comprising a pair of duplicate receiving units, each of said receiving units comprising a pair of similar receiving tubes and a receiver plate coil connected between the plates of the two receiving tubes comprised in said unit, a second winding constituting a second source of alternating current of supersonic frequency, the point of said second winding of potential mid-way between the potentials of its terminals being connected to the filaments of the tubes of both of said receiving units, the terminals of said second winding being respectively connected to the respective mid-points of said receiver plate coils, and a common power supply system for distributing alternating current power connected for supplying said first winding and said second winding with control electric energy for respectively actuating said generating units and said receiving units for maintaining the frequency and phase of said second source at said receiving station identical with the frequency and phase of said first mentioned supersonic source at said transmitting station.

WILLIAM ARTHUR LOTH. ARMAND JOSEPH GIVELET. 

